Piano ESP sends only recent stories to users by default. Also, Piano ESP excludes stories sent previously and stories that have been read by the user on the website. Please, be aware, that these parameters should be enabled in the following dynamic block settings:
It is also important to mention that ESP uses Content selection types and Fill up with rules, that you can also find and set up in the dynamic block settings:
So, when you send a test email with the 'Real data' option it would lead to the running of actual content selection types (personal recommendations, only the latest relevant content, no duplicates, etc.). It means that some template blocks may not have any content.
Also, you can select 'Latest' or 'Ordered' content selection type (these type picks-up rules that are more focused on the order of appearance in the RSS feed rather than on the users' interests) and send a test email with the indicated 'Real data' option. But keep in mind, advanced settings that were described above still may affect the content pulling to the dynamic block.
In light of the above, we recommend sending test emails with sample content selection to get the full view of the template structure and content with all blocks filled.